Module 5 · Biological Agents
5.4 Wood-Boring Insects — Active or Historic?
10 min read
Flight holes are permanent. A beetle infestation that ended in 1955 leaves exactly the same holes in 2026, and those holes have sold an enormous quantity of unnecessary treatment. The identification question — which species — matters far less than the activity question, and the activity question is answerable on site with a torch and a hand lens.
Learning objectives
By the end of this lesson you will be able to:
- Identify the main species from hole size, frass and timber type.
- Assess activity from the physical evidence rather than from the holes' existence.
- Recognise which species indicate an underlying moisture or decay problem.
- Advise proportionately, including advising that no treatment is required.
Key terms
- Flight hole
- The exit hole made by an emerging adult beetle. Permanent, and evidence only that a beetle once emerged — not that any are there now.
- Frass
- The bore dust and faecal pellets pushed out of the timber. Its texture and pellet shape are species-diagnostic, and fresh frass is the main activity indicator.
- Sapwood
- The outer, nutrient-bearing part of the timber. Most wood-boring beetles attack sapwood and leave heartwood alone.
- Emergence season
- Roughly May to August in Britain, when adults emerge. Live adults, fresh holes and fresh frass are most evident then.
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Read the rest of Biological Agents
Module 1 is open to everyone. The remaining six modules — building science, each damp mechanism in depth, meters and thermal imaging, the full inspection method, and report writing — are free too. We just ask for an email so you can pick up where you left off, and so we can send your certificate when you finish.